Security devices (e.g., security threads, strips and patches) are used widely in security documents such as banknotes, passports and other high value documents. Typically, they are incorporated into the security document during manufacture although in some cases they are adhered onto a surface of the document after manufacture of the document itself.
Efforts to increase the security of these devices have included the use of high value materials such as liquid crystal color shift materials, which are inherently complex and specialized. These high value materials are typically applied as a film or thin layer on a surface of a continuous polymeric web substrate during continuous web manufacturing processes. Many times, however, the high value material is hidden or obscured in areas on the web surface by the application of additional materials (e.g., printed information).
The present inventor has developed a method for reducing the amount of high value materials used in the manufacture of security devices, and thus the cost of manufacture, while avoiding degradation or obscuration of the high value material. By way of the inventive method, the high value material is applied to only a part of the security device, leaving remaining parts of the device available for one or more additional materials that do not impact upon the effect of the high value material. In an exemplary embodiment, the inventive method allows for a 50% reduction in the amount of high value materials used in the manufacture of these security devices.
The term “high value materials”, as used herein, is intended to mean special materials typically in the form of films (or film-like materials) that have a high value due to their inherent specialization and complexity. Examples of such high value materials include, but are not limited to, liquid crystal color shift films, dielectric layer color shift films, diffraction grating films, holographic films, micro-optic film materials that project synthetic images, and the like.
The present invention specifically provides a method for producing a composite web for making composite security devices, the method comprising:                (a) providing a first polymer film in the form of a first continuous web, wherein the first polymer film constitutes or embodies one or more first security features in the form of at least one high value material;        (b) providing a second polymer film in the form of a second continuous web, wherein the second polymer film constitutes, embodies, or is coated with one or more second security features;        (c) optionally applying one or more additional security features and/or one or more adhesives to one or opposing surfaces of the first and second continuous webs;        (d) in-line slitting the first continuous web into a number of relatively narrow width high value threads or strips;        (e) introducing separation between these relatively narrow width high value threads or strips;        (f) positioning and attaching the separated high value threads or strips to a surface of the second continuous web to form a continuous composite web; and optionally,        (g) laminating one or more protective layers to one or opposing surfaces of the continuous composite web.        
The resulting continuous composite web may then be slit into a number of composite security threads or strips, with each composite thread or strip having one of the narrow width high value threads or strips adhered to a surface thereof, the high value thread or strip positioned between, or aligned with one of the composite thread's or strip's longitudinal borders or edges.
The present invention further provides a composite security device, as described above.
Also provided are sheet materials that are made from or employ the inventive composite security device, as well as documents made from these materials. The term “documents”, as used herein designates documents of any kind having financial value, such as banknotes or currency, and the like, or identity documents, such as passports, ID cards, driving licenses, and the like, or non-secure documents, such as labels. The inventive optical system is also contemplated for use with consumer goods as well as bags or packaging used with consumer goods.
Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and accompanying drawings. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.